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At least 613 records · Page 34Linked to original sources
USGS2013

Net primary productivity of subalpine meadows in Yosemite National Park in relation to climate variability

Subalpine meadows are some of the most ecologically important components of mountain landscapes, and primary productivity is important to the maintenance of meadow functions. Understanding how changes in primary productivity are associated with variability in moisture and temperature will become increasingly important with current and anticipated changes in climate. Our objective was to describe patterns and variability in aboveground live vascular plant biomass in relation to climatic factors. We harvested aboveground biomass at peak growth from four 64-m 2 plots each in xeric, mesic, and hydric meadows annually from 1994 to 2000. Data from nearby weather stations provided independent variables of spring snow water content, snow-free date, and thawing degree days for a cumulative index of available energy. We assembled these climatic variables into a set of mixed effects analysis of covariance models to evaluate their relationships with annual aboveground net primary productivity (ANPP), and we used an information theoretic approach to compare the quality of fit among candidate models. ANPP in the xeric meadow was negatively related to snow water content and thawing degree days and in the mesic meadow was negatively related to snow water content. Relationships between ANPP and these 2 covariates in the hydric meadow were not significant. Increasing snow water content may limit ANPP in these meadows if anaerobic conditions delay microbial activity and nutrient availability. Increased thawing degree days may limit ANPP in xeric meadows by prematurely depleting soil moisture. Large within-year variation of ANPP in the hydric meadow limited sensitivity to the climatic variables. These relationships suggest that, under projected warmer and drier conditions, ANPP will increase in mesic meadows but remain unchanged in xeric meadows because declines associated with increased temperatures would offset the increases from decreased snow water content.

Western North American Naturalist↗
USGS2013

Rodent-Mediated Interactions Among Seed Species of Differing Quality in a Shrubsteppe Ecosystem

Interactions among seeds, mediated by granivorous rodents, are likely to play a strong role in shrubsteppe ecosystem restoration. Past studies typically consider only pairwise interactions between preferred and less preferred seed species, whereas rangeland seedings are likely to contain more than 2 seed species, potentially leading to complex interactions. We examined how the relative proportion of seeds in a 3-species polyculture changes rodent seed selectivity (i.e., removal) and indirect interactions among seeds. We presented 2 rodent species, Peromyscus maniculatus (deer mice) and Perognathus parvus (pocket mice), in arenas with 3-species seed mixtures that varied in the proportion of a highly preferred, moderately preferred, and least preferred seed species, based on preferences determined in this study. We then conducted a field experiment in a pocket mouse—dominated ecosystem with the same 3-species seed mixtures in both “treated” (reduced shrub and increased forb cover) and “untreated” shrubsteppe. In the arena experiment, we found that rodents removed more of the highly preferred seed when the proportions of all 3 seeds were equal. Moderately preferred seeds experienced increased removal when the least preferred seed was in highest proportion. Removal of the least preferred seed increased when the highly preferred seed was in highest proportion. In the field experiment, results were similar to those from the arena experiment and did not differ between treated and untreated shrubsteppe areas. Though our results suggest that 3-species mixtures induce complex interactions among seeds, managers applying these results to restoration efforts should carefully consider the rodent community present and the potential fate of removed seeds.

Utah↗
USGS2014

Demographic monitoring and population viability analysis of two rare beardtongues from the Uinta Basin

Energy development, in combination with other environmental stressors, poses a persistent threat to rare species endemic to energy-producing regions of the western United States. Demographic analyses of monitored populations can provide key information on the natural dynamics of threatened plant and animal populations and how these dynamics might be affected by present and future development. In the Uinta Basin in Utah and Colorado, Graham's beardtongue ( Penstemon grahamii ) and White River beardtongue ( Penstemon scariosus var. albifluvis ) are 2 rare endemic wildflowers that persist on oil shale habitats that are heavily impacted by current energy exploration and development and are slated for expanded traditional drilling and oil shale development. We described demographic characteristics and population viability for 2 populations of each species that have been monitored since 2004. First, we measured population size, survival rates, transitions between life stages, and recruitment by using individually marked plants at the 4 study areas. We then used matrix population models to determine stochastic population growth rates (λ) and the probability that each population would persist 50 years into the future, given current conditions. The 2 P. grahamii study plots had small populations, averaging 70 adult plants, and relatively constant and high survival in both vegetative and flowering plants. The 2 P. scariosus var. albifluvis study plots had populations that averaged 120 adult plants, with high and stable survival in flowering plants and variable survival in vegetative plants. Recruitment of new seedlings into all populations was low and variable, with most recruitment occurring in one or 2 years. Both P. grahamii populations had λ near 1.0 (stable). One P. scariosus var. albifluvis population appeared to be declining (λ = 0.97), whereas the other was increasing (λ = 1.16). Our analyses reveal populations that appear relatively stable, but that are susceptible to declines now and into the future. Increases in environmental variability, deterministic changes in habitat conditions or stressors, or a single catastrophic event could all have immediately deleterious impacts on the long-term growth trajectory of these populations.

Utah↗
USGS2014

Influence of nonnative and native ungulate biomass and seasonal precipitation on vegetation production in a Great Basin ecosystem

The negative effects of equid grazers in semiarid ecosystems of the American West have been considered disproportionate to the influence of native ungulates in these systems because of equids' large body size, hoof shape, and short history on the landscape relative to native ungulates. Tools that can analyze the degree of influence of various ungulate herbivores in an ecosystem and separate effects of ungulates from effects of other variables (climate, anthropomorphic disturbances) can be useful to managers in determining the location of nonnative herbivore impacts and assessing the effect of management actions targeted at different ungulate populations. We used remotely sensed data to determine the influence of native and nonnative ungulates and climate on vegetation productivity at wildlife refuges in Oregon and Nevada. Our findings indicate that ungulate biomass density, particularly equid biomass density, and precipitation in winter and spring had the greatest influence on normalized difference vegetation index (NDVI) values. Our results concur with those of other researchers, who found that drought exacerbated the impacts of ungulate herbivores in arid systems.

Nevada, Oregon↗
USGS2015

Precision of hard structures used to estimate age of mountain Whitefish ( Prosopium williamsoni )

The mountain whitefish ( Prosopium williamsoni ) is a widely distributed salmonid in western North America that has decreased in abundance over portions of its distribution due to anthropogenic disturbances. In this investigation, we examined precision of age estimates derived from scales, pectoral fin rays, and sagittal otoliths from 167 mountain whitefish. Otoliths and pectoral fin rays were mounted in epoxy and cross-sectioned before examination. Scales were pressed onto acetate slides and resulting impressions were examined. Between-reader precision (i.e., between 2 readers), between-reader variability, and reader confidence ratings were compared among hard structures. Coefficient of variation (CV) in age estimates was lowest and percentage of exact agreement (PA-0) was highest for scales (CV = 5.9; PA-0 = 70%) compared to pectoral fin rays (CV =11.0; PA-0 = 58%) and otoliths (CV = 12.3; PA-0 = 55%). Median confidence ratings were significantly different ( P ≤ 0.05) among all structures, with scales having the highest median confidence. Reader confidence decreased with fish age for scales and pectoral fin rays, but reader confidence increased with fish age for otoliths. In general, age estimates were more precise and reader confidence was higher for scales compared to pectoral fin rays and otoliths. This research will help fisheries biologists in selecting the most appropriate hard structure to use for future age and growth studies on mountain whitefish. In turn, selection of the most precise hard structure will lead to better estimates of dynamic rate functions.

Western North American Naturalist↗
USGS2015

Effects of ungulate disturbance and weather variation on Pediocactus winkleri: Insights from long-term monitoring

Population dynamics and effects of large ungulate disturbances on Winkler cactus ( Pediocactus winkleri K.D. Heil) were documented annually over a 20-year time span at one plot within Capitol Reef National Park, Utah. This cactus species was federally listed as threatened in 1998. The study began in 1995 to gain a better understanding of life history aspects and threats to this species. Data were collected annually in early spring and included diameter, condition, reproductive structures, mortality, recruitment, and disturbance by large ungulates. We used odds ratio and probability model analyses to determine effects of large ungulate trampling and weather on these cacti. During the study, plot population declined by 18%, with trampling of cactus, low precipitation, and cold spring temperatures implicated as causal factors. Precipitation and temperature affected flowering, mortality, and recruitment. Large ungulate disturbances increased mortality and reduced the probability of flowering. These results suggest that large ungulate disturbances and recent climate regimes have had an adverse impact on long-term persistence of this cactus.

Utah↗
USGS2015

Tree mortality in mature riparian forest: Implications for Fremont cottonwood conservation in the American southwest

Mature tree mortality rates are poorly documented in desert riparian woodlands. I monitored deaths and calculated annual survivorship probability (P s ) in 2 groups of large (27–114 cm DBH), old (≥40 years old) Fremont cottonwood ( Populus fremontii Wats.) in a stand along the free-flowing Yampa River in semiarid northwestern Colorado. P s = 0.993 year-1 in a group ( n = 126) monitored over 2003–2013, whereas P s = 0.985 year -1 in a group ( n = 179) monitored over the same period plus 3 earlier years (2000–2003) that included drought and a defoliating insect outbreak. Assuming P s was the same for both groups during the 10-year postdrought period, the data indicate that P s = 0.958 year -1 during the drought. I found no difference in canopy dieback level between male and female survivors. Mortality was equal among size classes, suggesting P s is independent of age, but published longevity data imply that either P s eventually declines with age or, as suggested in this study, periods with high P s are interrupted by episodes of increased mortality. Stochastic population models featuring episodes of low P s suggest a potential for an abrupt decline in mature tree numbers where recruitment is low. The modeling results have implications for woodland conservation, especially for relictual stands along regulated desert rivers.

Colorado↗
USGS2015

Estimating bighorn sheep (Ovis canadensis) abundance using noninvasive sampling at a mineral lick within a National Park Wilderness Area

Conservation of species requires accurate population estimates. We used genetic markers from feces to determine bighorn sheep abundance for a herd that was hypothesized to be declining and in need of population status monitoring. We sampled from a small but accessible portion of the population's range where animals naturally congregate at a natural mineral lick to test whether we could accurately estimate population size by sampling from an area where animals concentrate. We used mark-recapture analysis to derive population estimates, and compared estimates from this smaller spatial sampling to estimates from sampling of the entire bighorn sheep range. We found that estimates were somewhat comparable; in 2009, the mineral lick sample and entire range sample differed by 20 individuals, and in 2010 they differed by only one individual. However, we captured 13 individuals in the entire range sample that were not captured at the mineral lick, and thus violated a model assumption that all individuals had an equal opportunity of being captured. This eliminated the possibility of inferring a total population estimate from just animals visiting the mineral lick, but because estimates were relatively similar, monitoring at the mineral lick can provide a useful index for management and conservation. We compared our results to a radio-collar study conducted in 2003–2004 and confirmed that the population remained stable since 2004. Our population estimates were 78 (CI 62–114) in 2009 and 95 (CI 77–131) in 2010. Between 7 and 11 sampling dates were needed to achieve a CV of 20% for population estimates, assuming a capture probability between 0.09 and 0.13. We relied on citizen science volunteers to maximize data collection and reduce costs; 71% of all fecal samples were collected by volunteers, compared to 29% collected by paid staff. We conclude that our technique provides a useful monitoring tool for managers. The technique could be tested and applied in similar populations where animals congregate with high fidelity at a mineral lick or other area.

Colorado↗
USGS2015

Facing a changing world: Thermal physiology of American pikas ( Ochotona princeps )

American pikas ( Ochotona princeps ) are of concern with respect to warming montane temperatures; however, little information exists regarding their physiological ability to adapt to warming temperatures. Previous studies have shown that pikas have high metabolism and low thermal conductance, which allow survival during cold winters. It has been hypothesized that these characteristics may be detrimental, given the recent warming trends observed in montane ecosystems. We examined resting metabolic rate, surface activity, and den and ambient temperatures (T a ) of pikas in late summer (August 2011 and 2012) at 2 locations in the Rocky Mountains. Resting metabolic rate was calculated to be 2.02 mL O 2 · g -1 h -1 , with a lower critical temperature (LCT) of 28.1 ± 0.2 °C. No upper critical temperature (UCT) could be determined from our data; therefore, the estimated thermoneutral zone (TNZ) was 28.1 °C to at least 35.0 °C (upper experimental temperature). Pikas in this study showed the same bimodal above-talus activity patterns reported in previous studies. Den temperatures in Colorado were correlated with, but consistently lower than, current ambient temperatures. Wyoming den temperatures showed a weak correlation with T a 20 min prior to the current den temperature. This study is one of few to present data on the physiological response pikas may have to current warming conditions, and the first to perform metabolic measurements in situ. Our data support conclusions of previous studies, specifically MacArthur and Wang ( 1973 , 1974 ) and Smith ( 1974 ), which indicated American pikas may not have the physiological ability to cope with high Ta. Our results also highlight the importance of shaded regions below the talus rocks for behavioral thermoregulation by pikas.

Western North American Naturalist↗
USGS2015

Black-tailed and white-tailed jackrabbits in the American West: History, ecology, ecological significance, and survey methods

Across the western United States, Leporidae are the most important prey item in the diet of Golden Eagles ( Aquila chrysaetos ). Leporids inhabiting the western United States include black-tailed ( Lepus californicus ) and white-tailed jackrabbits ( Lepus townsendi i) and various species of cottontail rabbit ( Sylvilagus spp.). Jackrabbits ( Lepus spp.) are particularly important components of the ecological and economic landscape of western North America because their abundance influences the reproductive success and population trends of predators such as coyotes ( Canis latrans ), bobcats ( Lynx rufus ), and a number of raptor species. Here, we review literature pertaining to black-tailed and white-tailed jackrabbits comprising over 170 published journal articles, notes, technical reports, conference proceedings, academic theses and dissertations, and other sources dating from the late 19th century to the present. Our goal is to present information to assist those in research and management, particularly with regard to protected raptor species (e.g., Golden Eagles), mammalian predators, and ecological monitoring. We classified literature sources as (1) general information on jackrabbit species, (2) black-tailed or (3) white-tailed jackrabbit ecology and natural history, or (4) survey methods. These categories, especially 2, 3, and 4, were further subdivided as appropriate. The review also produced several tables on population trends, food habits, densities within various habitats, and jackrabbit growth and development. Black-tailed and white-tailed jackrabbits are ecologically similar in general behaviors, use of forms, parasites, and food habits, and they are prey to similar predators; but they differ in their preferred habitats. While the black-tailed jackrabbit inhabits agricultural land, deserts, and shrublands, the white-tailed jackrabbit is associated with prairies, alpine tundra, and sagebrush-steppe. Frequently considered abundant, jackrabbit numbers in western North America fluctuate temporally and spatially. We also reviewed methods used to investigate jackrabbit populations, including spotlight line transects, flushing transects, drive counts, pellet plot counts, collections, roadside counts, mark-recapture studies, and radio-telemetry studies. Our review of jackrabbit literature illustrates a number of deficiencies in our understanding of jackrabbits in general. As an example, a detailed quantitative description of habitat preferences is lacking, as is a thorough understanding of sympatric jackrabbit species interactions. Even the existence of the oft-cited jackrabbit “cycle” is a matter of debate. Survey methods generally do not address efficacy or accuracy in measuring jackrabbit density or abundance. In addition, there is a paucity of information about jackrabbits in the Mojave Desert, with no real understanding of home ranges, habitat preferences, and population dynamics or demographics in this region.

Arizona, California, Colorado, Idaho, Iowa, Kansas↗
USGS2016

Ecosystem engineering of harvester ants: Effects on vegetation in a sagebrush-steppe ecosystem

Harvester ants are influential in many ecosystems because they distribute and consume seeds, remove vegetation, and redistribute soil particles and nutrients. Understanding the interaction between harvester ants and plant communities is important for management and restoration efforts, particularly in systems altered by fire and invasive species such as the sagebrush-steppe. Our objective was to evaluate how vegetation cover changed as a function of distance from Owyhee harvester ant ( Pogonomyrmex salinus ) nests within a sagebrush-steppe ecosystem. We sampled 105 harvester ant nests within southern Idaho, USA, that occurred in different habitats: annual grassland, perennial grassland, and native shrubland. The influence of Owyhee harvester ants on vegetation was larger at the edge of ant nests, but the relationship was inconsistent among plant species. Percent cover was positively associated with distance from harvester ant nests for plant species that were considered undesirable food sources and were densely distributed. However, percent cover was negatively associated with distance-from-nests for patchily distributed and desirable plant species. For some plant species, there was no change in cover associated with distance-from-nests. Total vegetation cover was associated with distance-from-nests in the shrubland habitat but not in the 2 grasslands. The dominant plant species in the shrubland habitat was a densely distributed shrub (winterfat, Krascheninnikovia lanata ) that was defoliated by harvester ants. Our results suggest that Owyhee harvester ants increase spatial heterogeneity in plant communities through plant clearing, but the direction and magnitude of effect will likely be contingent on the dominant vegetation groups. This information may inform future management and plant restoration efforts in sagebrush-steppe by directly considering the islands of influence associated with harvester ant engineering.

Idaho↗
USGS2016

Aspects of the reproductive ecology of female turtles in New Mexico

Data on reproductive ecology of turtles in New Mexico are limited, and some species living there are among the least studied in the United States. We trapped 4 native species of turtles ( Apalone spinifera, Chrysemys picta, Pseudemys gorzugi, and Trachemys gaigeae gaigeae ) in the Rio Grande and Black River (Pecos River drainage) of New Mexico in June 2012 and 2013 to collect data on female reproductive ecology, including clutch size, egg size, timing of egg production, and percentage of gravid females. During our sampling, we found shelled eggs via X-radiography in only 3 native species: C. picta, P. gorzugi, and T. g. gaigeae. Clutch and egg sizes were within the range of previously reported values, although clutch size for P. gorzugi (10 eggs) is only the second published record for that data-deficient species. Clutch size increased with body size in T. g. gaigeae. We observed few differences between reproductive parameters for turtles in New Mexico and their conspecifics and congeners elsewhere in the United States, other than the observation that female C. picta may mature at smaller body sizes in New Mexico relative to other western populations elsewhere in its vast, primarily eastern North American range.

New Mexico↗
USGS2016

Habitat and fish assemblage associations and current status of northern leatherside chub Lepidomeda copei in western Wyoming

Human activities have extensively altered native fish assemblages and their habitats in the western United States. Conservation and restoration for long-term persistence of these fishes requires knowledge of their distributional patterns and life history requirements. Northern leatherside chub Lepidomeda copei (hereafter northern leatherside) is a cyprinid native to the Snake and Bear River Basins of Wyoming, Idaho, Nevada, and Utah, and it is believed to have declined in distribution relative to historical records. To address information gaps in the species' ecology and assess its status in the state, the objectives of this study were first to document the distribution (2010–2011) of northern leatherside in Wyoming and then to examine habitat factors related to the entire fish assemblage and to evaluate specific habitat associations of northern leatherside in the Bear River Basin, Wyoming. In the Bear River and Upper Snake River Basins, we documented the distribution of northern leatherside and compared it to the previously known distribution. Across the Bear River Basin, we used habitat measurements to assess abiotic features related to the distribution and abundance of northern leatherside. Northern leatherside was found across the Bear River Basin and was present in 2 streams each in the Upper Snake River and Green River Basins in Wyoming. Populations in Wyoming appear to represent the core of northern leatherside range, and our work provided a finer-scale delineation of the species' occurrence. Northern leatherside was collected from a variety of habitats, but multivariate analyses and occurrence modeling indicated it was associated with increased channel depth and depth variability, and positively associated with other native fishes (including mountain sucker Catostomus platyrhynchus, redside shiner Richardsonius balteatus, and speckled dace Rhinichthys osculus). These findings on the distribution and ecology of northern leatherside provide important new information to assist successful management and conservation efforts within Wyoming and across the species' range.

Wyoming↗
USGS2017

Functional traits and ecological affinities of riparian plants along the Colorado River in Grand Canyon

Trait-based approaches to vegetation analyses are becoming more prevalent in studies of riparian vegetation dynamics, including responses to flow regulation, groundwater pumping, and climate change. These analyses require species trait data compiled from the literature and floras or original field measurements. Gathering such data makes trait-based research time intensive at best and impracticable in some cases. To support trait-based analysis of vegetation along the Colorado River through Grand Canyon, a data set of 20 biological traits and ecological affinities for 179 species occurring in that study area was compiled. This diverse flora shares species with many riparian areas in the western USA and includes species that occur across a wide moisture gradient. Data were compiled from published scientific papers, unpublished reports, plant fact sheets, existing trait databases, regional floras, and plant guides. Data for ordinal environmental tolerances were more readily available than were quantitative traits. More publicly available data are needed for traits of both common and rare southwestern U.S. plant species to facilitate comprehensive, trait-based research. The trait data set is free to use and can be downloaded from ScienceBase: https://www.sciencebase.gov/catalog/item/58af41dee4b01ccd54f9f2ff and https://dx.doi.org/10.5066/F7QV3JN1

Arizona↗
USGS2017

Tolerance to disturbance regulated by attractiveness of resources: A case study of desert bighorn sheep within the River Mountains, Nevada

Human activity may mimic predation risks for wildlife by causing abandonment of foraging sites and increasing expenditure of energy. Animals that can tolerate nonlethal disturbance may minimize these fitness costs. We examine this aspect of the risk—disturbance hypothesis by first analyzing recent habitat use of desert bighorn sheep relative to areas of attraction and disturbance. We then compare and contrast sheep responses to differing levels of anthropogenic disturbance between 2 time periods, 30 years apart. Desert bighorn sheep were tolerant of suburban activity when a consistent forage resource (municipal grass) was provided. Males were more tolerant than females, and females returned to natural, steep areas during the birthing season. Increased recreation activity, specifically mountain bike use, may have resulted in avoidance by sheep of otherwise suitable habitat that had been occupied decades earlier, thereby reducing availability of limited habitat. Tolerance increased only when attractiveness was relatively high and decreased as perceived fitness decreased, supporting risk—disturbance theory.

Nevada↗
USGS2017

Between hot rocks and dry places: The status of the Dixie Valley toad

In Dixie Valley, Nevada, an isolated population of toads has been the subject of proactive conservation measures by the Nevada Department of Wildlife and the U.S. Fish and Wildlife Service since 2008 due to concerns about potential habitat degradation resulting from exploitation of nearby geothermal energy resources. These toads appear to belong within the Anaxyrus boreas species group but are commonly referred to as Dixie Valley toads (DVTs). The DVT is currently confined to an extremely narrow habitat range (370 ha) that is geographically isolated from any other A. boreas population. In this study, genetic variations in mitochondrial genes and 11 microsatellite loci were used to assess the affinities of DVTs in relation to members of the A. boreas species group. We compared results from DVTs with previously published data spanning much of the range of A. boreas in the United States and new data from a nearby toad population within Dixie Valley. Data from both mitochondrial DNA and microsatellites placed DVTs inside the A. boreas species group. In particular, DVTs fell into a cluster of A. boreas from Washington and California, along with other species from the A. boreas species group, namely A. nelsoni, A. canorus, and A. exsul. Genetic differentiation of DVTs was lowest between A. boreas populations in Washington and California. However, allele frequencies were significantly different between DVTs and all other populations, including a nearby locality within Dixie Valley. This genetic differentiation, along with the DVT's geographical isolation and restricted habitat, warrants recognition of the DVT as a distinct management unit.

Nevada↗
USGS2017

Estimating ages of Utah chubs by use of pectoral fin rays, otoliths, and scales

Utah chub Gila atraria is native to the Upper Snake River system in Wyoming and Idaho and to the Lake Bonneville Basin in Utah and southeastern Idaho. However, the Utah chub has been introduced into many other waterbodies in the western United States, where it competes with ecologically and economically important species. The objectives of this study were to evaluate between-reader precision and reader confidence in age estimates obtained from pectoral fin rays, lapilli (otoliths), asterisci (otoliths), and scales for Utah chubs collected from Henrys Lake, Idaho. Lapilli have been previously shown to provide accurate age estimates for Utah chubs; therefore, we sought to compare age estimates from fin rays, asterisci, and scales to those from lapilli. The between-reader coefficient of variation (CV) in age estimates was lowest and the percent of exact reader agreement (PA-0) was highest for pectoral fin rays (CV = 4.7, PA-0 = 74%), followed by scales (CV = 10.3, PA-0 = 52.3%), lapilli (CV = 11.6, PA-0 = 48.2%), and asterisci (CV = 13.0, PA-0 = 41.7%). Consensus age estimates from pectoral fin rays showed high concordance with consensus age estimates from lapilli. Our results indicate that pectoral fin rays provide the most precise age estimates for Utah chub. Pectoral fin rays are easily collected and processed and also provide age estimates without requiring fish sacrifice.

Western North American Naturalist↗
USGS2017

Landscape movements by two species of migratory nectar-feeding bats (Leptonycteris) in a northern area of seasonal sympatry

Animals often migrate to exploit seasonally ephemeral food. Three species of nectar-feeding phyllostomid bats migrate north from Mexico into deserts of the United States each spring and summer to feed on blooms of columnar cactus and century plants ( Agave spp.). However, the habitat needs of these important desert pollinators are poorly understood. We followed the nighttime movements of 2 species of long-nosed bats ( Leptonycteris yerbabuenae and L. nivalis ) in an area of late-summer sympatry at the northern edges of their migratory ranges. We radio-tracked bats in extreme southwestern New Mexico during 22 nights over 2 summers and acquired location estimates for 31 individuals. Both species cohabitated 2 major day roosts that were 30 km apart and in different mountain ranges, and individual bats sometimes moved between the roosts. Sampling was opportunistic and limited, but there were no obvious qualitative differences in observed patterns of movement between species or years, or among sex, age, and reproductive groups. Both species were observed foraging most often in the mountain range that had a relatively higher observed density of presumed food plants ( Agave palmeri ); when roosting in an adjacent mountain range, bats sometimes commuted >20 km one way to forage. Contrary to evidence indicating these species partition resources farther south in Mexico, our findings suggest that L. yerbabuenae and L. nivalis seasonally share common roost and food resources during late summer in this northern area of sympatry.

Western North American Naturalist↗